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EVALUATING TREES ON THE UNIVERSITY OF ARIZONA CAMPUS
Prepared by members of the University of Arizona Campus Arboretum Committee
Elizabeth Davison, Founding Director
TABLE OF CONTENTS
The UA Campus Arboretum is committed to preserving the University's unique trees and shrubs for their educational, historic, economical and aesthetic value. As a part of the larger Tucson urban forest, the campus trees are a resource for both the campus community and the University's neighbors and visitors. We are in agreement with the general concepts put forth by the Campus Comprehensive Plan that advocate for more shade, more attractive open spaces, and more use of outdoor areas.
Campus construction projects often call for removal or transplanting of trees. Many of them are old or stately. Some are rare. Others are common and easily replaced. It is impossible to save every tree, and it is impractical to try. Nonetheless, there is a growing interest in retaining as many of the older trees as possible as the campus expands. The UA Campus Arboretum is committed to helping in this process. How to prioritize? In response to several requests, we are submitting this document to help with the steps necessary for considering the value of the UA trees during planning, designing and constructing the facilities of the University of Arizona campus.
Much of the information in this paper relies on formulations and techniques found in the book Guide for Plant Appraisal, 9th edition (see attached sheets), developed by the Council of Tree and Landscape Appraisers. The Council of Tree and Landscape Appraisers is an organization housed within theInternational Society of Arboriculture. This book is used by professional plant appraisers to give a monetary value to a tree, a wood lot, or an entire recreational area (or campus). According to the book's preface, "Plant valuations are not limited to casualty situations but can include appraisals for tree inventories, real-estate transactions, plant condemnation actions, and insurance purposes."
We are not prepared to assign a monetary value to all trees on campus, at least not yet. The University of Arizona campus is a unique site, and the trees we own include dozens of unusual species (with some not at all available in the nursery trade). The oldest, rarest trees, and those with connection to UA history have intrinsic worth; they can not adequately be evaluated based on dollars alone. We do propose using the tools described in the Guide to Plant Appraisal to assist in giving a relative value by comparing the more common trees of identical species, or similar size, or by assessing objective criteria. Using the methods described in this book, it is possible to get a priority or relative value (and if necessary, a precise monetary value) for most of the more common UA trees.
The University of Arizona has roots that go deep into the early explorations of the southwestern deserts and establishment of scientific institutions like the Carnegie Desert Laboratory. On a campus where the purpose is mainly education and where the values include heritage (including its Land Grant status), it is important to recognize the aesthetic value of rich green spaces, the rarity of a species, or the history of the tree's life on that site. Thus simply asking "how much to buy a new one?" is not adequate. We can ask questions such as the following. Are other plants of this species represented elsewhere on campus? Is this plant's size important? Does this species have special educational, historic, commemorative, or ecological value? Is the relationship to the site important? Is germplasm (seeds or cuttings) restricted because of international botanical laws? We may find that some very common species have grown into trees that are huge. Some of the rarer trees are quite small. Some trees are in protected sites and do not normally survive in Tucson. Finally, some trees are worth only the time and fuel to remove them and plant a more interesting species. Some examples include: 1. We have the very first Rhus lancea (African sumac) planted in Tucson. While the species is considered by some to be weedy and invasive, this individual has merit for its age and connection to the UA through former President Shantz. 2. The largest Crape Myrtle in Tucson is in the Park Ave. green belt. No one would say this tree is rare; it is common in the nursery trade. Yet its size and health give it a priority. 3. Any mesquite installed in the last 10 years is expendable, unless it is clearly strong and stately (eg., NW of McKale Parking Garage, E. of McKale). For the most part, the species has hybridized, so that even seeds collected by a nursery from a "native" mesquite have genetic traits from the South American species. These traits include large thorns and a tendency to blow over in high winds if the root zone is restricted by paving or incorrect irrigation.
The University of Arizona Campus Arboretum has designated 20 trees as Heritage Trees on the campus. They are rare species, the largest in the SW or in Arizona, were planted by former faculty or students, or relate in some way to the heritage of the University. In addition, within the Alumni Plaza we have designated Alumni Plaza Heritage Trees: three boojums, one senita, one organ pipe in the Krutch Garden, and the baobab tree next to the Administration Building. Heritage Trees and Alumni Plaza Heritage Trees would stand at the top of the list as being valuable and worth retaining in place as a part of a project design.
At a second level, the Valuable Trees are worth saving for their educational value. See Attachment. They have less connection to UA history, but are valuable for their size, elegance, or rarity. In many cases they are the only representative of the species on campus, and usually the only one in Tucson. They may be currently unavailable from the originating country. They may represent an historic Tucson landscape style, prevalent in the earlier part of the century. They may be less xeric, but provide deep shade. They are part of the urban forest in Tucson. In evaluating the University of Arizona's trees for the planning process on new construction projects, we will first determine whether they are Heritage Trees or Valuable Trees. The Campus Arboretum is committed to working with Planning, Design, and Construction, and Facilities Management to retain these important trees on site. Protecting trees during construction is more than just leaving them in place, and involves fencing off the root zone, adequate irrigating, mulching, and pruning. We think it is possible to develop successful Tree Protection guidelines for the University of Arizona Campus Arboretum. We would encourage RFPs to incorporate language that suggests the value of protecting trees during construction. Transplanting does not always work. For some trees on the UA Campus, transplanting may be an option. However, it can be costly, and there may not be a high rate of success. Before attempting to "save" a tree, we suggest using the methods as detailed in the Guide to Plant Appraisal.
This process will allow general comparisons for more common trees, both to dollar value and to possibilities for replacement. The Council on Tree and Landscape Appraisers (hereafter called the Council), recognizes that trees can be evaluated in different ways depending on the purpose and audience. They have defined three methods: 1. Cost Approach - how much does the tree add to the landscape or property (considering its size and health), or how much would it take to replace it (considering growth and depreciation)? How much would it take to repair it? This approach links directly to the market value of trees as commodities. Nursery prices and availability are factors. 2. Income Approach - how much will the trees add to the value of an Income-Producing Property? Timber stands, orchards, or a cluster of rental vacation cabins are classic examples. In Tucson, shady parking lots or plazas may draw more shoppers, and the income can be measured. 3. Sales Comparison Approach - how much more value does a tree-filled property have compared to a similar piece without trees? Because plants and landscapes have value, market assessments or property sales can be used to extract the contributory value of value of plants. This method is used in conjunction with Real Estate agents and appraisers, and is more complex than the first two. To assign a value to the more common trees on the UA campus, we propose using the Cost Approach, modified by considerations as to context of the tree at the University of within the Southwest.
According to the Guide for Plant Appraisal, four primary factors help in assessing the value by the Cost Approach: Species, Condition, Size, and Location. These factors can be objectively evaluated, and can work additively to arrive at a dollar valuation. We will address these factors and explain how they influence a tree's value.
1. TREE SPECIES - Is this a good species for this area or for the site? Species Ratings vary geographically. The guidelines suggest that native species get higher ratings than imported species. Considerations include whether the species is tolerant of the climate, the soils, and the water availability. A 100% Species Rating could be given to an indigenous native tree tolerant of a site's environment. On the UA campus, a low Species Rating would be given to a tree that is native to the Pacific Northwest, no matter its condition. On the other hand, a medium Species Rating would be given to a non-native tree that can tolerate extreme heat and compacted soil, and survive on scheduled irrigation. Some non-natives might get a moderately high rating because of their general adaptation to campus conditions.
2. TREE CONDITION - Does this tree have strong structural integrity and good vigorous health? The plant's existing condition is the most reasonable gauge for determining the Condition Rating. Even if the tree species is known to be weak or to be susceptible to insect infestations, we give the Condition as a "real time" assessment. We do not make allowances for the causes of the Condition rating (this comes later). We assign a score from 1 - 4 on the following. Structural integrity includes the determination of root conditions and stability; trunk soundness, decay, or cavities; then branch conditions, soundness, and attachment. We consider tree structure in relation to its potential to fail and damage something. Plant Health and vigor can be evaluated by the annual shoot growth from preceding years. We also look at leaf discoloration and size, decay, dieback, disfiguration from disease or insects, etc. Problems with infrastructure will cause a lower rating. Insufficient room to expand, soil compaction from parked trucks, damage from construction and other "urban" issues can have an influence. Human-caused damage plays a part in reducing the value of a tree. We give the roots a 1-4 rating for Structural Integrity and for Health. We do the same for trunk, scaffold branches, small branches, and foliage. Add scores, and convert to percentage to determine the Condition Rating. On the UA Campus, a tree that is dying back (regardless of reason) will have a lower Condition Rating than the same species which is not suffering. Comparing two of the same species, a more vigorous individual will rate higher than another. Age does not influence rating. A Heritage or Valuable tree might have any Condition Rating.
3. TREE SIZE - Is this tree large and imposing or small and full of potential? We compute two things: 1) cross-sectional trunk area of the tree in question, and 2) its dollar value. To link size to money, we compare trees on a site to "dollar per size unit" value of the same species for sale in a local nursery. In both the landscape tree and the nursery tree, trunk area is determined from circumference, and the trunk is considered to be a circle. The Guide to Plant Appraisal contains guidelines for measuring and formulas for determining multi-trunk areas, trees on slopes, leaning trees, etc. We determine the unit value for the landscape tree by comparing it with a nursery tree's value. If the nursery tree with 10 sq inches of trunk cross-sectional area sells for $300, we assign the landscape tree a value of $30 per square inch of trunk area. If the landscape tree has 50 sq in. of cross-sectional trunk area, its value is $1500. We have two answers: area and dollar value. If the tree is not available anywhere locally, we can go further afield to get prices. Trees that are not available at all can be measured for size and compared to others of their species, but not given a monetary value. Their rarity or history becomes more important. On the UA Campus, based on trunk area, smaller recently-planted trees may be valued very close to the replacement cost. Older trees (same species), with diameters of over 6" will be geometrically more valuable as they increase in size. This is particularly true as tree size grows beyond the largest available box in local nurseries.
4. TREE LOCATION - How does the tree perform in the landscape? Location Rating is the average of three sub-ratings: Site, Contribution, and Placement. This helps determine how the tree has been designed into the landscape, how much it contributes, and whether it is "working" to enhance that landscape. We rate from 10 to 100% on the following. Site (relative market value within the city, county, region) implies that trees on a well-maintained site are worth more than the same species on an unkempt property. This implication is controversial. Money talks. Contribution (functional and aesthetic value) considers things trees do: shade, screening, dust control, cooling, defining vistas, crowd control, and all aesthetic and historic factors. Placement (can it perform its function?) addresses the design/siting of the tree so that it has the best chance to provide the shade, control the crowds, or screen the view. A tree that frames a building or blocks an unsightly view will get a different rating than one that does not. We average the three ratings to determine a final Location Rating for the tree. On the UA Campus, trees that are sited so as to provide shade for walks, buildings, or hardscape will have a higher Location Rating than the same species situated too close to a building. Trees that have space to grow and "show their stuff" get a higher rating than those that are hidden. The trees in the Park Avenue Green belt have high Site and Contribution percentages, but a lower Placement percentage, since many of them are becoming large and crowded.
Assume the goal is to find the approximate value of a tree which we intend to destroy, but replace with a nursery tree after a construction project. Using the Cost Method of Plant Appraisal as defined in the Guide for Plant Appraisal, we make a calculation based on all of the ratings. 1. Assume the tree is larger than any tree in a nursery. The calculation of the value of a tree would begin by using the price of the largest size of the species available in the nursery trade. This is combined with a cost for installation to give a Installed Plant Cost. 2. We divide the Installed Plant Cost by the trunk area (in square inches) of the boxed nursery tree. This gives a $$ cost / sq inch for the nursery tree. 3. We multiply that $$ cost / sq inch of nursery tree by the Size of the tree in question. We have measured this in the field. This gives a hypothetical cost for a perfect full grown tree at today's prices. 4. We then multiply that value for the perfect full grown tree by all the combined percentage ratings from Species, Condition, and Location. Typically this reduces the value. We might factor in a cost to remove the original damaged tree. We might adjust for special value to the University or special circumstances. 5. The net result is a value for the full grown tree that we are considering for removal. We often find that we are destroying something worth $ 5,000 so that we can replace it with a $375 nursery tree. Or we are spending $10,000 to move a tree that will not survive the move.
The University of Arizona Campus Arboretum will work to see that Heritage and Valuable trees are allowed to remain in place. They are the first priority. Rare trees are valuable for their educational value. Other large and stately trees are valuable for their size and their shade, and should be carefully considered. Mature trees on this campus are an important part of the larger Tucson urban forest. Their values may be incalculable by the process outlined in Guide for Plant Appraisal. However the Guide for Plant Appraisal's Tree Valuation techniques can be the basis for evaluating the remaining 75% of more common trees which may be impacted by campus construction. We have provided this overview to illustrate that there are documented, and well utilized, techniques for determining the value of trees. In addition to assigning a dollar value to an individual tree on the UA campus, the process of Tree Valuation might be used to augment real estate worth for the total University acreage, to determine the value per tree as used in climate mitigation, to evaluate the dollar value per square foot of shade, to compare utility use in shaded areas vs areas having fewer trees, and to assess student interest per dollar value of the campus trees. The possibilities are endless. We hope this overview on evaluating trees will assist our colleagues in the planning process as new construction projects come along.
Please feel free to contact the Director, Dr. Tanya M. Quist at 621-7074 or firstname.lastname@example.org
EVALUATING TREES ON THE UNIVERSITY OF ARIZONA CAMPUS September 2002 Prepared by members of the UA Campus Arboretum Committee and Elizabeth Davison, Founding Director
In response to a request from Mr. Robert Smith of Planning, Design, and Construction, The University of Arizona Campus Arboretum provides this document to describe methods by which the campus trees may be evaluated. On the University of Arizona campus, rare trees are valuable for their educational value. Mature trees on this campus are an important part of the larger Tucson urban forest, and are valuable for their size and their shade. Still other trees are valuable for their connection to UA heritage, were donated by graduating classes, or are a component of botanical research. As described herein, Tree Valuation techniques can be the basis for evaluating 75% of more common trees which may be impacted by campus construction. We have provided this overview to illustrate that there are documented, and well utilized, techniques for determining the value of trees. The process begins by pricing a small tree at a nursery. That monetary value is adjusted based on the tree's condition, size, location, and other objective factors. Certified Arborists and Certified Plant Appraisers are qualified to make these calculations, but the process is straightforward. The UA Campus Arboretum Committee is committed to working with other campus units in determining the best methods of keeping the campus shady and the tree collection intact.